I find a lot of sites feel like they're overtuning their recommendation engines, to the detriment of using the site. YouTube is particularly bad for this - given the years of history and somewhat regular viewing of the site, I feel like it should have a relatively good idea of what I'm interested in. Instead, the YouTube homepage seems myopically focused on the last 5-10 videos I watched.
This is because they're not trying to give you stuff you'd generally like given your entire history. The recommendation feature powers the part of YouTube that auto-plays the upcoming video. So e.g. if I go and view Russian dashcam videos they're going to automatically play more of them, even though I've shown no prior interest in that topic. Having two systems for recommendations would introduce a lot of UI complexi…
Do you mean, in terms of implementation or for the user? Because as the later, I think the two are already conceptually different (homepage vs next video), so I don't see how just feeding it different videos would make it more complex.